Concomitant loss of dynorphin, NARP, and orexin in narcolepsy

Abstract

Background: Narcolepsy with cataplexy is associated with a loss of orexin/hypocretin. It is speculated that an autoimmune process kills the orexin-producing neurons, but these cells may survive yet fail to produce orexin.

Objective: To examine whether other markers of the orexin neurons are lost in narcolepsy with cataplexy.

Methods: We used immunohistochemistry and in situ hybridization to examine the expression of orexin, neuronal activity-regulated pentraxin (NARP), and prodynorphin in hypothalami from five control and two narcoleptic individuals.

Results: In the control hypothalami, at least 80% of the orexin-producing neurons also contained prodynorphin mRNA and NARP. In the patients with narcolepsy, the number of cells producing these markers was reduced to about 5 to 10% of normal.

Conclusions: Narcolepsy with cataplexy is likely caused by a loss of the orexin-producing neurons. In addition, loss of dynorphin and neuronal activity-regulated pentraxin may contribute to the symptoms of narcolepsy.

Figure 1

Prodynorphin and NARP co-localize with orexin. A) In coronal hypothalamic sections from a control subject, most neurons containing orexin-IR also produce prodynorphin mRNA (black circles) and are mainly located in the lateral and posterior hypothalamic areas (LHA and PHA) above and around the fornix (fx). A few neurons apparently containing only orexin (white circles) or prodynorphin (grey circles) are scattered within this region, and a separate group of neurons producing only prodynorphin mRNA lie in the paraventricular nucleus of the hypothalamus (PVH). B) Neurons double-labeled for orexin-B and NARP (black circles) have a similar distribution. This region also contains a few neurons apparently containing only orexin-B (white circles) or only NARP (grey circles). The PVH contains many cells producing only NARP. Other abbreviations: 3V, third ventricle; opt, optic tract; LT, lateral tuberal nucleus; VMH, ventromedial hypothalamic nucleus; DMH, dorsomedial hypothalamic nucleus; TM, tuberomammillary nucleus; SO, supraoptic nucleus; st, stria terminalis; IGP, internal globus pallidus; MMC, mammillary nucleus, magnocellular part; SUM, supramammillary nucleus; cp, cerebral peduncle.

Figure 2

Loss of prodynorphin and NARP in narcolepsy. A) Sections from a subject with narcolepsy show a marked reduction in the number of neurons labeled for orexin (white circles). Within the orexin field, the number of neurons expressing prodynorphin mRNA (grey circles) is also reduced, but the paraventricular nucleus still contains a moderate number of prodynorphin-labeled cells. B) This individual also has a substantial loss of neurons double-labeled for orexin-B and NARP (black circles) within the orexin neuron field. This region also contains a few cells apparently containing only orexin-B (white circles) or only NARP (grey circles), but the PVH still contains a large number of neurons producing NARP alone.